1. Field of the Invention
The present invention relates generally to a cam and cam follower arrangement and more specifically to a pre-loaded cam follower arrangement which exhibits both a long working life and which can be efficiently manufactured.
2. Brief Description of the Related Art
In certain types of machinery such as those which use helical cams and the like, it is necessary to use a cam follower which grips the cam and ensures that the cam profile is faithfully followed. One example of this type of cam follower is found in U.S. Pat. No. 5,676,006 issued to Marshall on Oct. 14, 1997. This patent discloses a preloaded-cam follower ram assembly for reshaping containers. The contents of this patent are hereby incorporated by reference thereto. Features of this arrangement are depicted in FIGS. 1-3.
As will be appreciated, this cam following arrangement includes first and second cam followers 10, 12. The second of these cam followers (12) is mounted on an end section 14 which is integral with a ram arrangement generally denoted by the numeral 16. The first cam follower (10), on the other hand, is supported on a pivotal member 18 that is operatively connected to the end of the end section 14 via a pivot pin 20. A cantilevered spring 22 is used to bias the pivotal member 18 to rotate in a direction which causes the first cam follower 10 to approach the second cam follower 12, and thus produce a nipper-like action that clamps the followers 10, 12 against the sides of cam member (not shown) when in use.
A further arrangement which has been developed is such that the cantilevered spring is replaced with a pack of conical springs. This arrangement is depicted in FIGS. 4-12. This arrangement has been found to extend cam follower life. As will be best appreciated from FIG. 4, this arrangement features a fork construction 23 which is configured to have a slide block (slider) 24 slidably received therein. The fork fingers 26 and the slider 24 have a tongue (261) and groove (262) arrangement (see FIG. 5 for example) which retains the slider 24 within the fork 23 while permitting the required reciprocal movement.
The ends of the fork fingers 264, which are located at the open end of the fork 23, are connected by an end cap 28. A conical spring pack 30 (see FIG. 12) is disposed between the end cap 28 and one end of the slider 24 to bias the slider 24 away from the end cap 28 and toward the closed end 231 of the fork 23.
However, as will be appreciated, very tight tolerances must be maintained to ensure that the slide block or slider 24 is freely movable in the axial direction, but does not have any clearance that permits rocking of the cam follower on the cam face under dynamic loading. To achieve this, the clearance required must be held in multiple planes, and is provided by the tongue in groove arrangement.
The end cap 28 has the ability, when connected to the ends of the forks, to either hold the fingers 26 in a slightly inwardly flexed condition or in a slightly outwardly flexed state, if necessary in order to provide the required clearances.
However, a problem occurs if the fingers of the fork twist as a result of processes which are applied during production. For example, during heat treatment which follows the machining processes and which is necessary to harden the surfaces that are in sliding contact with one another, the metal undergoes expansions and contractions which will unpredictably result in minor distortions (such as the above-mentioned twisting) and which cannot be corrected via the use of the end cap.
While this arrangement shown in FIGS. 10-12, has proven very effective if successfully manufactured, a drawback arises that the number of units which must be scraped or re-worked due to the above-mentioned distortions can be so high as to render the manufacture of this type of arrangement excessively time consuming and therefore expensive.